1. Field of the Invention
The present invention relates to a fixing device, an image forming apparatus using the fixing device, and a fixing method. Particularly, the present invention relates to a fixing device used to fix a toner image in an electrophotographic image forming apparatus.
2. Description of the Related Art
In an electrophotographic image forming apparatus, it is common to cause a powdery coloring material called “toner” to electrostatically adhere to a recording medium, and to heat and press the toner to fix the toner to the recording medium. Examples of the recording medium include a recording medium made of paper, a recording medium made of resin and used for an OHP or the like, and other types of recording media.
As a commonly-used conventional fixing method, there is a roller nip type method in which a recording medium having a toner image transferred thereonto is nipped and conveyed by two rollers, or a belt nip type method in which the recording medium is nipped and conveyed by an endless belt and rollers (Japanese Laid-Open Patent Publication No. 2012-068665 (Document 1), Japanese Laid-Open Patent Publication No. 09-160405 (Document 2), Japanese Laid-Open Patent Publication No. 2006-154608 (Document 3) and the like).
Document 1 describes a method for fixing a toner image by sequentially arranging a fixing device of belt nip type and a fixing device of roller nip type, and heating a recording medium to different temperatures by these fixing devices. Each of Documents 2 and 3 describes a method for fixing a toner image by nipping and conveying a recording medium by a heated belt in a fixing device of belt nip type. When a recording medium is conveyed with a roller or a belt being pressed in contact with the recording medium, the toner is heated and a releasing agent included in the toner seeps out, so that a toner image is fixed and at the same time the separation property between the toner image and the roller or the belt can be achieved (hereinafter also simply referred to as “fixation and separation property”).